For a moment, it seemed like Jason Reitman could do no wrong, following up his excellent directorial debut, “Thank You for Smoking,” with one great movie after the next, and earning a quartet of Oscar nominations in the process. But even the best filmmakers are capable of making bad movies, and though “Labor Day” isn’t a complete failure, it’s the director’s weakest film by a country mile. Based on the 2009 novel by Joyce Maynard, the movie represents a major departure for Reitman, who’s made a name for himself telling stories with a dark comedic bite. That trademark humor isn’t present in “Labor Day,” instead replaced by the kind of gooey sentimentalism that you’d be more likely to find in a Nicholas Sparks adaptation, which leads me to wonder what Reitman was even thinking.

Set in a quaint New England town during Labor Day weekend in 1987, the film stars Kate Winslet as Adele, a shut-in single mother on the verge of a nervous breakdown. During a rare excursion outside to take her teenage son Henry (Gattlin Griffith) clothes shopping for the new school year, they’re approached by a wounded stranger named Frank (Josh Brolin), who takes Adele and Henry hostage and holes up in their rundown house with the intention of making a run for it at nightfall. A convicted murderer who escaped from the hospital while recovering from an emergency appendectomy, Frank insists that there’s more to the story, and as they spend more time with the supposedly dangerous fugitive, he turns out to be a pretty nice guy. So when Frank ends up staying the next day to do some repairs around the house, Adele and Henry don’t complain, and before long, he’s accepted as a part of the family, serving as a father figure to Henry and passionate lover to the fragile Adele.

The whole movie is narrated by a grown-up Henry (Tobey Maguire) as he recounts the events of that weekend, and if you think the idea of a woman falling in love with the very convict holding herself and her son hostage sounds absurd, it’s made even more so by the fact that it takes place over just four days. It’s essentially a trashy romance novel disguised as an Oscar prestige movie – the kind of story that sets back feminism several decades by suggesting that a woman could be this helpless without a strong man around the house to take care of her. The entire premise is ridiculous, but there’s one scene in particular – where Frank teaches Adele how to make a peach pie à la the pottery-wheel sequence in “Ghost” – that is so awkwardly erotic that it sets the stage for the rest of the film, especially considering Henry is right there with them the whole time.

Though the first act is fairly good, staged more like a kidnapping thriller than a sappy romance, it eventually devolves into the melodramatic nonsense mentioned above. The constant tonal changes don’t help, and the film grinds to a halt every time the main story is interrupted by oddly placed flashback sequences that tease what really happened to land Frank in prison. It’s hard to imagine how much worse “Labor Day” might have been without Winslet and Brolin in the lead roles, because their performances are the only thing separating this from your average Lifetime movie of the week. It’s admirable of Reitman to want to try something different, but even guys like Martin Scorsese have learned that it’s better just to stick to what you’re good at, and if Reitman has proven anything over the past eight years, it’s that he’s so much better than this.